this is a bug i encountered after upgrading to 4.10 rc3, it wasn't there in rc2.

i don't know which part of kde is relevant here (bugzilla told me to guess a component so i picked plasma which might be unrelated); the behaviour i see is this:

computer boots fine and i can log into a kde plasma desktop session as usual, the programs i used last time start (dolphin, konsole for example). but if i now want to launch other programs, either by clicking a file in dolphin, or by clicking a program icon, or from the command line, these programs simply dont start. when trying to launch from the command line, i get an error message:

QDBusCOnnection: session D-Bus connection before QCoreApplication. Application may misbehave.

i tried with vlc, kate, systemsettings, ksystemlog, digikam ... all these programs don't start, it seems to be a general thing. non-kde programs like firefox or nautilus started from the command line do work, however.

i also tried loggin into a ubuntu session with its unity desktop. from there i could launch digikam, for example.
 
i dont know which other information would be useful for tracking this bug but will look it up if someone points me in the right direction.

Reproducible: Always

Steps to Reproduce:
see above
Actual Results:  
programs dont start

Expected Results:  
programs do start